DESIGN STRATEGY FOR RECYCLED AGGREGATE CONCRETE

DESIGN STRATEGY FOR RECYCLED AGGREGATE CONCRETE

RAEng Frontiers Champion Project:

Recycled Aggregate Concrete in South East Asia

Nikola TošićUniversitat Politécnica

de Catalunya

nikola.tosic@upc.edu

CONTENTS

▸ Intro to CEN prEN1992 and fib Model Code 2020

▸ RAC provisions in prEN1992 and MC2020

▸ Background to RAC code provisions

▸ Implications for design and future work

1.Intro to CEN prEN1992 & fib MC2020

Intro to prEN1992 and MC2020

CEN – European Committee for Standardization

EU + Iceland + Norway + Switzerland + UK + North Macedonia ++ Serbia + Turkey

Intro to prEN1992 and MC2020

EN 1992 – Design of Concrete StructuresEN 1992-1-1:2004 Part 1-1: General rules and rules for buildingsEN 1992-1-2:2004 Part 1-2: General rules - Structural fire designEN 1992-2:2005 Part 2: Concrete bridges - Design and detailing rulesEN 1992-3:2006 Part 3: Liquid retaining and containment structures

Links to other EN standards:EN 196, EN 197 – Methods of testing cement; CementEN 206+A1 – Concrete – Part 1: Specification, performance, production and conformityEN 10080 – Steel for the reinforcement of concreteEN 12620 – Aggregates for concreteEN 13670 – Execution of concrete structures

Intro to prEN1992 and MC2020

Revision of the Eurocodes

Intro to prEN1992 and MC2020

Revision of the Eurocodes

https://eurocodes.jrc.ec.europa.eu/showpage.php?id=23

Intro to prEN1992 and MC2020

Revision of the Eurocodes: prEN1992-1-1 & prEN1992-1-2

▸ CEN Enquiry: September–December 2021

▸ Target date of availability of 2nd generation EN 1992: March 2023

▸ Date of publication – national choice (National Annexes!)

▸ Target Date of Availability of last 2nd gen. Eurocodes: March 2026

▸ Target Date of Withdrawal of 1st gen Eurocodes: March 2028

Intro to prEN1992 and MC2020

International Federation for Structural Concrete – fib

Euro-International

Committee for Concrete

Comité euro-internationale du béton1953

CEB

International Federation

for Prestressing

Fédération internationale

de la précontrainte

1952

fib

David Fernández-Ordóñez, 2018

Intro to prEN1992 and MC2020

International Federation for Structural Concrete – fib

David Fernández-Ordóñez, 2018

Intro to prEN1992 and MC2020

Evolution of Model Codes

David Fernández-Ordóñez, 2018

Intro to prEN1992 and MC2020

Task Group 4.7: Structural Applications of Recycled AggregateConcrete – Properties, Modelling, and Design

https://www.fib-international.org/commissions/com4-concrete-concrete-technology.html

2.RAC provisions in prEN1992 & fib MC2020

RAC provisions in prEN1992 and MC2020

Current basis: EN 12620 & EN 206+A1

▸ Only coarse RA▸ Composition-based classification▸ Future – performance-based classification?

https://www.gov.il/BlobFolder/reports/aggregates/en/04%20Sanchez-

%20EN%2012620%20Aggregates%20for%20concrete.pdf

RAC provisions in prEN1992 and MC2020

Current basis: EN 12620 & EN 206+A1

▸ Only coarse RA▸ Low substitution ratios▸ Assuming no change in properties/not taking into account any change

RAC provisions in prEN1992 and MC2020

Current situation:

▸ “High collection rates of well-segregated CDW are achieved…but the market uptake of recycled materials is really low; large storage areas at treatment plants have essentially become temporary landfills”

▸ Motivation: increase the use of RA in structural applications!

[1]

[2]

RAC provisions in prEN1992 and MC2020

RAC provisions in prEN1992 and MC2020

RAC provisions in prEN1992 and MC2020

MC2020 section 12

3.Background to RAC code provisions

RAC provisions in prEN1992 and MC2020

Background: significant amount of research performed overprevious decades on all levels – from material to structural

[3]

[4]

[5]

[6]

[7]

Background documents

RAC provisions in prEN1992 and MC2020

Fabienne Robert, 2021

Choice of main variable – N.3

▸ Definition of αRA

▸ Future: changes to EN 206?

▸ Future: LoA with more variables?

[8]

RAC provisions in prEN1992 and MC2020

Choice of main variable – MC2020

▸ τTRA (=αRA) and τRCA

▸ MC2020 does not rely on EN 206

RAC provisions in prEN1992 and MC2020

Density

• volumetric vs. mass replacement ratio

Δ𝜌RAC = 𝜌ag ∙ 𝑉ag − 𝜌ag ∙ 𝑉ag ∙ 1 − 𝛼V,RA + 𝜌c ∙ 𝑉ag ∙ 𝛼V,RA = (𝜌c−𝜌ag) ∙ 𝑉ag ∙ 𝛼V,RA

𝛼RA =𝜌c ∙ 𝑉ag ∙ 𝛼V,RA

𝜌ag ∙ 𝑉ag 1 − 𝛼V,RA + 𝜌c ∙ 𝑉ag ∙ 𝛼V,RA=

𝜌c ∙ 𝛼V,RA

𝜌ag ∙ 1 − 𝛼V,RA + 𝜌c ∙ 𝛼V,RA

𝛼V,RA =𝜌ag ∙ 𝛼RA

𝜌c + (𝜌ag − 𝜌c) ∙ 𝛼RA

𝜌RAC = 2.50 − 0.22 ∙ 𝛼RA[9]

RAC provisions in prEN1992 and MC2020

Compressive strength

• Input parameter in the code!

• No observed difference in statistical distribution vs. NAC

• <= C50/60 (~fcm,max = 60 MPa)

[10]

RAC provisions in prEN1992 and MC2020

Modulus of elasticity

• 𝐸cm = 𝑘E ∙ 𝑓cmΤ1 3

• 𝐸cm = 𝑘E − 𝑘E − 𝑘RA ∙ 𝛼RA ∙ 𝑓cmΤ1 3

• Experimental database

• prEN1992: 𝐸cm = 𝑘E ∙ 1 − 0.25 ∙ 𝛼RA ∙ 𝑓cmΤ1 3

• MC2020: 𝐸cm = 𝑘E ∙ 1 − 1 −7100

𝑘E∙ 𝛼𝑅𝐴 ∙ 𝑓cm

Τ1 3

[9]

RAC provisions in prEN1992 and MC2020

Tensile strength

prEN 1992: 𝑓ctm = 0.3 ∙ 𝑓ckΤ2 3 = 0.3 ∙ 𝑓cm − 8 Τ2 3; for concrete strength class ≤ C50/60

and 𝑓ctm = 1.1 ∙ 𝑓ckΤ1 3; for concrete strength class > C50/60

MC2020: 𝑓ctm = 1.8 ∙ ln 𝑓ck − 3.1 = 1.8 ∙ ln 𝑓cm − 8 − 3.1; for all strength classes

𝑓ctm = 𝑎 ∙ 1 − 1 −𝑏

𝑎∙ 𝛼𝑅𝐴 ∙ 𝑓ck

Τ2 3

Experimental database

For low RA content no change!

[9]

RAC provisions in prEN1992 and MC2020

Stress–strain relationship

•𝜎c

𝑓cm=

𝑘∙𝜂−𝜂2

1+ 𝑘−2 ∙𝜂

• 𝜀c1 = 0.7 ∙ 𝑓cmΤ1 3 ≤ 2.8‰

• 𝜀cu1 = 2.8 + 14 ∙ 1 − Τ𝑓cm 108 4 ≤ 3.5‰

• Increases for RAC observed in experiments

• 𝜀c1 = 1+ 0.33 ∙ 𝛼RA ∙ 0.7 ∙ 𝑓cmΤ1 3 ≤ 2.8‰

• 𝜀cu1 = 1 + 0.33 ∙ 𝛼RA ∙ 2.8 + 14 ∙ 1 − Τ𝑓cm 108 4 ≤ 3.5‰

[9]

RAC provisions in prEN1992 and MC2020

Fracture energy

• prEN 1992: not treated

• MC2020: 𝐺𝐹 = 85 ∙ 𝑓ck0.15

• Experimental database:

• 𝐺𝐹 = 1 − 0.4 ∙ 𝛼RA ∙ 85 ∙ 𝑓ck0.15

Shrinkage

• Strong increase for RAC!

• RECYBETON: 𝜀cs,RAC 𝑡, 𝑡𝑠 = 1+ 0.82 ∙ 𝛼RA ∙ 𝜀cs 𝑡, 𝑡s

• Tošić et al. 2018: 𝜀cs,RAC 𝑡, 𝑡s = 𝜉cs,RAC ∙ 𝜀cs 𝑡, 𝑡s =100∙𝛼CRA

𝑓𝑐𝑚

0.30∙ 𝜀cs 𝑡, 𝑡s ≥ 𝜀cs 𝑡, 𝑡s

• 𝜀cs,RAC 𝑡, 𝑡𝑠 = 1+ 0.8 ∙ 𝛼RA ∙ 𝜀cs 𝑡, 𝑡s

RAC provisions in prEN1992 and MC2020

[11]

[12]

[12]

[9]

Creep

• Strong increase for RAC!

• RECYBETON:𝜑RAC 𝑡, 𝑡0 = 1 + 0.9 ∙ 𝛼RA ∙ 𝜑 𝑡, 𝑡0

• Tošić et al. 2019a: 𝜑RAC 𝑡, 𝑡0 = 𝜉cc,RAC ∙ 𝜑 𝑡, 𝑡0 = 1.12 ∙100∙𝛼CRA

𝑓cm

0.15∙ 𝜑 𝑡, 𝑡0 ≥ 𝜑 𝑡, 𝑡0

• 𝜑RAC 𝑡, 𝑡0 = 1 + 0.6 ∙ 𝛼RA ∙ 𝜑 𝑡, 𝑡0

RAC provisions in prEN1992 and MC2020

[11]

[13]

[13]

[9]

Durability

• prEN 1992: If Exposure Resistance Classes (ERC) are not used, “traditional” cover

recommendations are given

• ERCs not envisioned by MC2020

• Qualitative literature review:

• Carbonation – cmin,dur,NAC + 5 mm

• Chloride ingress – cmin,dur,NAC + 10 mm

RAC provisions in prEN1992 and MC2020

Flexural and shear strength

• Basing calculations on fcm – no need to modify flexural strength models

• For shear there is a need to increase γC!

• Members not requiring shear reinforcement:

• 𝜏Rd,c ≥ 𝜏Rdc,min ⟹0.66

𝛾C∙ 100 ∙ 𝜌l ∙ 𝑓ck ∙

𝑑dg

𝑑

Τ1 3

≥11

𝛾C∙

𝑓ck

𝑓yd

𝑑dg

𝑑

• 𝑑dg = 16 mm+ 𝐷lower ≤ 40 mm for 𝑓ck ≤ 60 MPa

• 1 − 0.2 ∙ 𝛼RA ∙0.66

𝛾C∙ 100 ∙ 𝜌l ∙ 𝑓ck ∙

𝑑dg

𝑑

Τ1 3

≥ 1 − 0.2 ∙ 𝛼RA ∙11

𝛾C∙

𝑓ck

𝑓yd

𝑑dg

𝑑

• ddg limited to 16 mm

RAC provisions in prEN1992 and MC2020

Deflection control

• Decrease modulus; increase creep and shrinkage – not enough

• Decrease tension stiffening (Tošić et al. 2019b)

• 𝑎 = 𝑎1 ∙ 1 − 𝜁 + 𝑎2 ∙ 𝜁; 𝜁 = 1 − 𝛽tRA ∙𝜎sr

𝜎s

2

• 𝛽tRA = 1.0 for single, short − term loading

• 𝛽tRA = 0.25 for sustained or repeated loading

• Expression for L/d can be used as long as modulus, creep and shrinkage are considered

RAC provisions in prEN1992 and MC2020

[14]

Bond and anchorage/lap lengths

• No differences observed relative to NAC

RAC provisions in prEN1992 and MC2020

[9]

4.Implications for designand future work

Implications for design and future work

Example: 6-m one-way slab in a residential building, As for ULSShear strength:

Deflection control:

[15]

0.0

1.0

2.0

3.0

4.0

15 17 19 21 23 25

VR

d/V

Ed

L/d

NAC RAC 0.2

RAC 0.4

C25/30

0.0

1.0

2.0

3.0

4.0

15 17 19 21 23 25

VR

d/V

Ed

L/d

NAC RAC 0.2

RAC 0.4

C50/60

0.0

0.5

1.0

1.5

2.0

15 17 19 21 23 25

a/a

lim

L/d

NAC

RAC 0.2

RAC 0.4

C25/30

0.0

0.5

1.0

1.5

2.0

15 17 19 21 23 25

a/a

lim

L/d

NAC

RAC 0.2

RAC 0.4

C50/60

[15]

Implications for design and future work

Directions for future work

Punching: critical for RAC use in residential and office buildingsExisting research scarce or not fully representative

Carbonated RA: easier mix design, improvement of RAC fresh-state and hardened properties; structural behaviour?

Prestressed RAC: existing research scarce

Innovative reinforcements/concretes: FRC, FRP, 3DPC, etc.

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Mater. Struct. 2021, 64, 119–125

THANK YOU FOR YOUR ATTENTION!

RAEng Frontiers Champion Project:

Recycled Aggregate Concrete in South East Asia

Nikola TošićUniversitat Politécnica

de Catalunya

nikola.tosic@upc.edu